This is a divisional of application Ser. No. 11/888,725, filed Aug. 2, 2007, now U.S. Pat. No. 7,394,724, which is a continuation-in-part of application Ser. No. 11/595,276, filed Nov. 9, 2006, now U.S. Pat. No. 7,423,934, which is a continuation-in-part of application Ser. No. 11/546,599 filed Oct. 12, 2006, now U.S. Pat. No. 7,372,774, which is a continuation of application Ser. No. 11/200,264, filed Aug. 9, 2005, now U.S. Pat. No. 7,123,548, issued Oct. 17, 2006, and the entirety of each of the foregoing applications and patent is incorporated herein by reference.
The present invention relates to a system for three dimensional multiple signal tracking, and reconstruction for use in connection with search and rescue, surveillance, storm and severe weather alerting, animal and bird migration, subsurface mapping, anti-terrorism, conventional warfare, etc.
Analog beamforming and antenna steering using loop, parametric and/or phased arrays, are methods employed for direction finding of acoustic and electromagnetic waves belonging to quasi-continuous signals. In one approach, a directional antenna (such as a parasitic array or loop antenna) is rotated towards the source for maximum reception. The detector may be a single receiver, as in the case of electromagnetic devices, or might be human ears receiving the output of two microphones mounted in the centers of large megaphones. The antenna's ‘beam’ could also be steered at a given frequency of operation by artificially introducing appropriate time delays into the detected signals from different antenna elements. These analog forms of beamforming were employed in World War II (radar and acoustics), for tracking aircraft and for transmitter hunting, and traditionally by radio amateurs in hunting hidden transmitters in practice for emergencies for sport, and for the elimination of undesired signals.
The time of arrival method has also been applied to locating sources of short duration signals, such wave pulses generated by earthquakes, shocks, blasts from explosions, cell phones, etc. Time of arrival techniques generally seek absolute and arrival time differences between signal arrivals at antenna transducer elements. Such systems typically obtain information from two or more antennas to obtain directions of incoming signals and employ triangulation techniques to estimate points of origins.
For quasi-continuous signals, certain beamforming and beam steering methods use fixed antenna arrays of transducer elements and digital signal sampling and processing to convert signal conditioned antenna output signals into digitized time series. These methods generally do not require antennas to be rotated, but instead typically make use of second order statistical functions obtained from cross-correlations and cross-spectral densities of time series of the different antenna elements. The second order statistical procedures allow for the determination of preferred signal directions and signal power spectra. Artificial channel time delays using digital processing can be used to numerically steer “antenna beams” and can also incorporate antenna beam modifications for adaptive processing and removal of undesired sources.
In contrast, the present system is based upon the creation and manipulation of signal vectors providing for the construction of mathematical models of physical wave fields at or in the vicinity of the antenna.